Method for increasing the bearing capacity of foundation soils for built structures

ABSTRACT

A method for increasing the bearing capacity of foundation soils for built structures consisting of providing a plurality of holes spaced from each other deep in the soil, and injecting into the soil, through the holes, a substance which expands as a consequence of a chemical reaction, with a potential increase in volume of at least five times the volume of the substance before expansion. The expansion of the substance injected into the soil produces compaction of the contiguous soil.

BACKGROUND OF THE INVENTION

The present invention relates to a method for increasing the bearingcapacity of foundation soils for built structures, including buildings,roadway slabs, airport runaways and equipment supporting slabs.

Any building requires the foundation soil to have a sufficient bearingcapacity to support it. Otherwise, the settling of the foundation soilleads to the failure of the overlying building, regardless of whetherthe settling occurs in the uppermost or in the deep layers.

Before erecting any building, the bearing capacity of the soil istherefore estimated according to the weight or load which the buildingwill apply to the soil, even using, if necessary, appropriate soilresearch, such as for example geological and geotechnical research.

In order to ensure the stability of the structure, the optimumdimensions of the foundations and their rigidity are calculated and thedepth of the foundations is also determined, adequately balancing theirweight in relation to the bearing capacity of the soil and alwaysmaintaining a good safety margin. In case of error, the building may infact fail.

Often, however, the bearing capacity of the foundation soil is notsufficient, since the soil is compressible, as in the case of filled-inland, non-consolidated land, land with decomposing organic layers, peatyland, swampy land, land with considerable variations in water content,flooded or washed-out land with voids or with non-uniform orinsufficiently aggregated masses, land with interstitial voids, etcetera; or the building is very heavy and requires a greater bearingcapacity than the actual bearing capacity of the foundation soil.

Various conventional systems ensure in any case the stability of thebuilding. Generally, these systems tend to directly transfer the weightof the building to the deeper and adequately solid soil layers or tospread the load over a wide ground surface, such as for example themethod consisting in driving piles or micropiles and the like into thefoundation soil. This method can be used both before and afterconstruction.

Of course, the driving of piles and micropiles or the like after theconstruction of the building is extremely complicated and expensive.

Conventional methods also cope with any subsidence of the building afterits construction, such as for example the method described in U.S. Pat.No. 4,567,708, which entails the injection of an expandable substancebeneath the building to fill the interstices which have formed and havecaused the subsidence and in order to recover the subsidence of thebuilding, or other lifting methods.

In the method disclosed in the above-cited patent, as well as in otherlifting systems, however, the foundation soil is not treated; at themost, one acts on the surface layers of the soil, and therefore if theunderlying soil has not settled enough, further subsequent subsidence ofsaid building will occur over time.

A method for ground consolidation using, an expandable substance, inwhich the expansion time is controlled to be slow or very slow, is knownfrom the document DE-A-33 32 256.

SUMMARY OF THE INVENTION

A principal aim of the present invention is to solve the above problemsby providing a method capable of ensuring the stability of builtstructures, including buildings, roadway slabs, airport runaways andequipment supporting slabs, by adequately treating the foundation soilin order to increase its bearing capacity. The term “foundation soil” isintended to designate that part of the soil having influence on theoverlying built structure or that the direct or indirect influence ofthe built structure (J. Collas and M Harvard, Manuale di Geotecnica,Faenza Editrice S. P. A., 1986).

Within the scope of this aim, an object of the present invention is toprovide a method which does not require the use of cement, concrete, ormetal structures driven into the ground, such as piles, micropiles,cement injections, very deep foundations, etcetera.

Another object of the present invention is to provide a method which issimple and easy to perform and can be adopted to increase the bearingcapacity of foundation soils both before and after construction of thebuilding.

This aim, these objects, and others which will become apparenthereinafter are achieved by a method for increasing the bearing capacityof foundation soils for built structures, according to the presentinvention, comprising the steps set forth in claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention willbecome apparent from the following detailed description of a preferredbut not exclusive embodiment of the method according to the invention,illustrated only by way of non-limitative example in the accompanyingdrawings, wherein:

FIG. 1 is a schematic view of the injection of the expandable substancethrough holes formed in the soil;

FIGS. 2 and 3 are views of the result of the expansion of the expandablesubstance when the substance is injected whilst the tube used forinjection is gradually retracted upwards, respectively with pauses atintermediate depth levels or with a continuous motion;

FIG. 4 is a view of the result of the expansion of the injectedsubstance in the case of sequential injections performed with differenttubes, inserted in different holes, in points spaced from each other andat different depths;

FIG. 5 is a schematic view of an injection operation, according to theinvention, with constant monitoring of the sinking recovery of abuilding foundation;

FIGS. 6-8 are comparative diagrams of dynamic penetrometric testscarried out on a soil area treated according to the invention;

FIG. 9 is a sectional view of a soil area treated in accordance with theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method according to the present invention substantially consists informing in the soil a plurality of holes 1 which, if one must act onexisting buildings, may or may not pass through the foundation, atdifferent depths and preferably with a distance between two contiguousholes 1 which can vary between 0.5 m and 3 m.

The holes 1 can have variable dimensions according to requirements andcan be provided substantially vertically or at an angle with respect tothe vertical.

The depth of the holes may also vary according to requirements, as willbecome apparent hereinafter.

Tubes 2 are then inserted or driven into the holes 1 and a substance 3expanding as a consequence of a chemical reaction between thecomponents, with a potential volume increase of at least five times thevolume of the substance before expansion, is injected into the soilthrough said tubes. The expression “potential volume increase” relatesto the volume increase of the substance as a consequence of an expansionoccurring unhindered at atmospheric pressure.

High expansion coefficients of 20-25 times the initial volume or evenhigher such as 30-33 may be preferred.

The expandable substance is conveniently constituted by a mixture ofexpandable polyurethane foam, preferably a closed-cell polyurethanefoam. This substance can be constituted, for example, by a two-part foammixed inside a mixing unit 4 connected to the injection tubes 2. Thefirst component can be a mixture of polyols comprising a polyetherpolyol and/or a polyester polyol, a catalyst, such as RESINOL AL 643produced by the Dutch company Resina Chemie, and water. The water in thecomposition may be 3.44% by weight. The second component can be anisocyanate MDI, such as URESTYL 10 manufactured by the same company. Themixing of these two components produces an expandable polyurethane foamthe density whereof, at the end of expansion, varies according to theresistance opposed by the soil adjacent to the injection region.

The mixture may expand up to about 33 times its initial volume and thereaction time is of about 3-6 seconds, as it appears from the technicalspecifications of the manufacturer.

It is of course also possible to use other expandable substances havingsimilar properties without thereby abandoning the scope of theprotection of the present invention.

According to requirements, the expandable substance can be injectedthrough the holes 1 formed beforehand in the soil in a single injectionstep, as shown in FIGS. 1, 2, and 3, starting from the bottom, whilstthe injection tube is gradually retracted upwards, optionally withintermediate pauses, as shown in FIG. 2, so as to obtain differentcolumns of hardened and expanded substance, or the substance can beinjected, optionally by performing sequential injections at fixed anddifferent depths in points which are three-dimensionally and uniformlyspaced from each other so as to obtain regions of expanded and hardenedsubstance within the foundation soil, as shown in particular in FIG. 4,according to requirements and according to the geologicalcharacteristics of the soil. In this last case, the tubes used forinjection are left in the soil.

Once the substance 3 has been injected, since it has also penetrated inany voids and fractures of the soil thanks to its fluidity, expandingwith great force and speed in all directions, it generates a force whichcompacts and compresses the soil all around, eliminating by compressionor filling all voids and microvoids, even extremely small ones,expelling most of the water impregnating the soil, possiblyagglomerating loose parts (granules and noncohesive parts) until a massof soil is obtained which, throughout the treated layer, can no longerbe compressed in relation to the weight that it has or will have tobear.

It should be noted that the expandable substance injected at differentdepths, in appropriately calculated points having a specific distancefrom each other, or along ascending lines, during expansionautomatically flows towards the more compressible points, which as suchoffer less resistance to the expandable substance. In this manner, theregions which most need treating are automatically treated moreintensely, without leaving spaces with untreated regions.

The immediate nature of the expansion of the injected substance alsoallows to delimit the expansion region rather precisely, thus allowingto localize very well, in the intended points, the effect to beproduced. The intense pressure applied by the injected substance to thesurrounding soil is in fact due to the expansion caused by the chemicalreaction and is not caused by hydraulic pressure. The expandablesubstance is injected through a hydraulic pressure which, however, onlyhas the purpose of introducing the substance in the chosen points.

The immediate reaction of the injected substance, in terms of expansionand curing, prevents its migration to faraway areas, where a slowreacting substance may instead arrive. In fact, the slower the expansionreaction is the farther the substance arrives, to the detriment of theprecise delimitation of the expansion effect and with consequentincrease of the injection substance consumption.

Advantageously, since in the conditions of the invention theconsolidation has a focused effect with low substance consumption,injection tubes may be used providing sufficient injection substanceflow rates which have an inner diameter, for example of 10 mm, thusbeing easily insertable into and retractable from the soil. Tubediameters being smaller or larger by some millimeters are also usable.Anyway employing tubes with much larger diameters, of about 2 cm ormore, difficult to drive into the soil, for obtaining high substanceflow rates is not necessary.

To efficiently localize the effect of the consolidation, the injectionmay be carried out, with intermediate pauses. For example injectionperiods of 15 seconds may be alternated with pauses of 1-2 seconds oreven longer. The durations of the active injection and respectively ofthe alternating pause periods are in fact selectable to be the moresuitable considering factors such as the injection depth, the injectionsubstance composition the length and the cross section of the injectiontubes.

For obtaining a more rapid expansion reaction of the injected substancewithout having to switch to other compositions, where necessary, it ispossible to raise by heating the temperature of the substance justbefore the injection operation.

As regards the hole depth, two different methods can be performed.

A first method consists in treating the entire thickness of the soillayers which are compressible or have a low bearing capacity, so as toperform consolidation up to the solid horizon of the layers having asufficient bearing capacity, regardless of their depth. The solidhorizon can be detected by means of geotechnical research conducted onthe soil.

The second method instead consists in treating a layer of soil which,for reasons related to technical and/or economic convenience, does notreach down to the identified solid horizon, which might be located at anexcessive depth, but is in any case thick enough to distribute theoverlying weight over a wider surface. The layer of soil treated withthe method according to the invention, by constituting a sufficientlycompact, solid, and in any case light layer, can be effectively andbroadly supported by the underlying layers of soil, even if those layerswould not otherwise have a sufficient bearing capacity.

Until now, injection depth of up to 6 m have been successfullyexperimented, but with adapted tube cross-sections and accuratelycontrolled substance injection flow rates, greater injection depths maybe attained.

The expansion of the injected substance following the chemical reactionof its components is very fast and develops a very high expansion force:up to 40 tons per square meter or even higher.

During injection, the level of the overlying building or of the surfacesoil can be constantly monitored by means of a laser level 5 or anothersystem (see FIG. 5). When the apparatus 5 indicates that the building orthe soil surface begins to rise, this generally means that thecompaction of the soil, in three dimensions all around the injectionpoint, has reached very high levels which are generally higher than therequired minimum values.

Through the constant monitoring operation, the precise moment when thesoil begins rising at a precise spot, due to the narrowly focusedexpansion force, and further the exact amount of the lifting areaccurately detected and may be controlled in real time.

The mass of injected substance, by reacting chemically, in fact expandswith great force in all directions, and when the apparatus detects evena small rise at the surface, this means that the expandable substancehas encountered less resistance in expanding in the vertical directionwith respect to all other directions and that therefore the soil lyingbelow and around the injected substance withstands and “rejects” all theweight (which is dynamic and therefore multiplied) not only of theentire mass of soil (and of any building) which rests staticallythereon, but also of all the surrounding mass displaced (by friction andcohesion) at a load diffusion angle which is usually calculated ataround 30° and is simply inverted. The raised soil, too, undergoescompression.

By repeating this operation at different depth levels (spaced byapproximately 1 meter from each other, but variably according to thekind of soil and to the bearing capacity to be obtained), at each level,a greater bearing capacity is obtained than the required one. By actingin this last manner and by performing continuous injections along risingcolumns, wherein tree-like shapes are formed with a very irregularconfiguration, with protrusions, bumps, and projections even ofconsiderable size produced by the different resistance of the soil tocompaction and to the possible presence of interstices or fractures inthe soil, in any case the entire mass and the treated layer of soil arecompressed, packed and compacted; the water content decreasesconsiderably; and the soil becomes a valid foundation soil adapted tostably support the building which lies above or is to be built.

The expandable substance can have a density varying indeed according tothe resistance opposed by the surrounding soil to its expansion. In mostcases, density can vary between 100 kg/m³ and 300 kg/m³. There may alsobe higher densities, since the density of the expanded substance isdirectly proportional to the resistance which it encounters to itsexpansion. The compression resistance of the expanded substance itselfis a function of density.

A substance with a density of 100 kg/m³ offers a resistance ofapproximately 14 kg/cm², whilst at a density of 300 kg/m³ compressionresistance is approximately 40 kg/cm². These values are far higher thanthose normally required for a foundation soil. In any case, where highercompression resistance values are required, even at different depths ofthe same soil, there is also a greater weight and therefore a higherresistance to expansion; accordingly, a denser and therefore strongermaterial forms automatically.

In any case, it is possible to momentarily add weight to a soil surfaceor to a building.

In practice, the injected and hardened expanded substance does notsupport the overlying building on its own, though helping to achievethis purpose; the weight of the building is effectively supported by thefoundation soil treated with the method according to the invention.

In practice it has been observed that the method according to theinvention fully achieves the intended aim and objects, since it allows,in a very simple, rapid, effective, and final manner, to increase thebearing capacity of foundation soils until they fully comply withconstruction requirements.

Typically, in what seems to be a general trend in ground consolidationtechniques, see for example the document DE-A-33 32 256, a very rapidexpansion, with very high expansion coefficients, creating rapidlyincreasing pressures in the treated soil, is purposely avoided, since itwas shown to provoke unwanted, mainly vertical, fissures in the treatedmass ground.

In the conditions of the invention, however, it has surprisingly beennoted that fissures occurring between soil masses, not only do notaffect the soil compaction, but can in fact be advantageously exploited.

Technical tests and studies, carried out on built lots where theconsolidation method of the invention has been used, have demonstratedthat the expansion of the injected material occurs first in directionswhere the soil offers less resistance, but only for a limited extent. Inthe case of a built spot this happens, in the first place, laterally tothe foundation and not in the vertical direction, where the weight ofthe building acts.

Only after the ground compaction degree is such as to provide aresistance to the lateral expansion forces well exceeding the weightforce exerted by the building, a vertical force is obtained such as toraise the foundation and the building. In fact it is not only the weightof the building which has to be compensated for, but also otherresistant forces, such as part of the weight of adjacent constructions,lateral friction forces and the flexural strength of the built structureitself.

While an immediate reaction of the injected material, in terms ofexpansion and solidification, may provoke indeed fissures between soilmasses forced to move with respect to each other by rapidly increasing,strong forces, a certain quantity of the injected substance appears infact to fill up the fissures so as to “weld” satisfactory the soilmasses, at least in the area to be consolidated, which is immediatelyclose to the injection site and under the foundation of the builtstructure. For exemplification see FIG. 9, where a “welded” fissure mayclearly be seen.

Penetrometric tests, the results whereof are shown in the diagrams ofFIGS. 6-8, have been carried out both under built spots treated with theconsolidation method according to the invention, after a soil liftinghas been sensed by the level apparatus, and laterally thereto, in closevicinity, at about 20 cm from the foundation.

From these diagrams showing comparatively the soil bearing capacitybefore consolidation (the not shadowed prisms) and after theconsolidation (the shadowed prisms), clearly appears that the mainconsolidation occurs under the foundation, between 120 and about 300 cmof depth (FIG. 6), while at only 20 cm laterally from the foundation,the consolidation appears, at the same depths as before, significantlydiminished (FIG. 7).

It is believed that this clearly shows the focused effect of theconsolidation carried out according to the invention which practicallyprovides a noteworthy reinforcement of mainly the soil under thefoundations.

The diagram of FIG. 8, drawn in the condition where an amount ofexpandable substance has been injected which has not provoked anydetectable lifting reaction of the soil under the building foundation,shows that in fact, laterally, at only 20 cm from the foundation,practically no effective soil compaction has occurred which would haveallowed generation of the vertical force necessary to the lifting andthereby also limiting the area where fissures may occur.

The method according to the invention has successfully been applied toconsolidate the ground and to compensate subsidences under heavilyloaded foundations in airports, such as those of the runaways, inindustrial and commercial constructions such as those of roadways andequipment supporting slabs, as well as under very old, historicbuildings and at archaeological sites.

Checkings of treated sites have been made recently, and have all givensatisfactory results. The inspections have been carried out inaccordance with a procedure approved by the French Control InstituteSOCOTEC consisting substantially in injecting, at a site selected by aninspector in a treated zone, at random, a small quantity of theinjection substance (about 20% of the quantity initially injected). Theresult has been considered positive if the injection triggered at leasta minimum lifting effect of the soil surface.

The method thus conceived is susceptible of numerous modifications andvariations, all of which are within the scope of the inventive concept;all the details may furthermore be replaced with other technicallyequivalent elements.

What is claimed is:
 1. A method for increasing the bearing capacity offoundation soils for built a structures comprising: providing aplurality of holes spaced from each other, under the foundation of abuilt structure, deep in the foundation soil; injecting into thefoundation soil, through said holes, a substance which expands as aconsequence of a chemical reaction; producing compaction of thefoundation soil contiguous to the injection one due to the expansion ofsaid substance injected into the soil; constantly monitoring levelvariations of the soil and/or built structures overlying the injectionzone to detect the moment when the built structures and/or the soilsurface, overlying injection zone, begins to raise which is the momentin which the compaction of the foundation soil has reached levelsgenerally higher than a required minimum value at which the soil lyingbelow and around said injection zone withstands and rejects dynamic andstatic weights exerted thereon by said built structures and by overlyingand adjacent soil masses, and wherein the expansion of the injectedsubstance is cry fast with a potential increase in volume of theexpanded substance being at least five times the volume of the substancebefore expansion.
 2. A method according to claim 1, wherein theinjecting step is repeated at different depth levels for producingcompaction of the masses or layers of treated soil.
 3. A methodaccording to claim 2, wherein said different depth levels are spaced byapproximately 1 m from each other, at each level a greater bearingcapacity than the required minimum value being obtainable.
 4. A methodaccording to claim 1, wherein said monitoring step is performed with alaser level apparatus.
 5. A method according to claim 2, wherein saidholes are provided vertically, the injection steps being performedcontinuously along rising columns wherein tree-like shapes are formedwith a very irregular configuration with protrusions, bumps andprojections of considerable size produced by different resistance tocompaction of the soil, and by the presence of interstices or fracturesin the soil.
 6. A method according to claim 5, wherein an entirethickness of the soil layers which are compressible or have low bearingcapacity is treated so as to perform consolidation up to the solidhorizon of the layers having a sufficient bearing capacity regardless ofthe depth at which the solid horizon is located.
 7. A method accordingto claim 6, wherein the expandable substance is selected from substancesadapted to produce immediate expansion.
 8. A method according to claim7, wherein the expandable substance comprises a mixture of twocomponents, the first being a polyether polyol and/or a polyestherpolyol, a catalyst and water, and the second being the isocyanate MDI.9. A method according to claim 5, wherein the distance between twoadjacent holes is between 0.5 m and 3 m.
 10. A method according to claim9, wherein said holes are provided at an angle with respect to thevertical.
 11. A method according to claim 2, wherein the injection stepcomprises several active injection phases alternated with suitablepauses.
 12. A method according to claim 1, wherein the injectionsubstance is heated just before the injection step.
 13. A methodaccording to claim 8, wherein the water content is of 3.44%, by weight.14. A method according to claim 11, wherein in the injection step, tubesare used through which the expandable substance is injected into thesoil, the tubes having an inner diameter of about 10 mm.
 15. The methodof claim 2, wherein the built structures include any of: buildings,roadway slabs, airport runaways, and equipment supporting slabs.
 16. Amethod according to claim 6, wherein the expandable substance is asubstance comprising a mixture of polyols and an isocyanate MDI.
 17. Amethod for increasing the bearing capacity of foundation soils for builtstructures comprising: providing a plurality of holes spaced from eachother deep in the foundation soil; providing an expandable substancewith very fast expansion time and with a potential increase in volume ofthe expanded substance being at least five times the volume of thesubstance before expansion; injecting into the soil, through said holes,said substance which expands as a consequence of a chemical reaction,the injection being performed continuously along rising columns;producing compaction of the soil contiguous to each substance injectionzone due to expansion of said substance injected into the foundationsoil which forms, along said columns, tree-like shapes with irregularconfiguration including protrusions, bumps and projections produced bydifferent resistance to compaction of the foundation soil and due tovoids, interstices or fractures present under said structure and intothe foundation soil; and constantly monitoring level variations of thesoil surface and/or built structure overlying the injection zone todetect a moment when the built structure and/or the soil surface,overlying said injection zone, begins to raise which is the moment whenthe compaction of the soil has reached levels generally higher than arequired minimum value at which the soil lying below and around saidinjection zone withstands and rejects dynamic and static weights exertedthereon by said built structures and by and adjacent soil masses. 18.The method of claim 17, wherein said holes are provided in thefoundation soil to have a direction selected to be any of a verticaldirection and a direction forming an angle with respect to the verticaldirection.
 19. The method of claim 18, wherein the built structuresinclude any of: buildings, roadway slabs, airport runaways, andequipment supporting slabs.
 20. A method for increasing the bearingcapacity of foundation soils for built structures comprising: providinga plurality of holes spaced from each other, under the foundation of abuilt structure, deep in the foundation soil; providing an expandablesubstance with very fast expansion time and with a potential increase involume of the expanded substance being at least five times the volume ofthe substance before expansion; injecting into the soil, through saidholes, said substance which expands as a consequence of a chemicalreaction; producing compaction of the soil contiguous to the substanceinjection zone through expansion of said substance injected into thefoundation soil until the soil compaction reaches levels which aregenerally higher than a minimum compaction value required to provide abearing capacity of the foundation soil suitable to withstand an dynamicand static weight exerted thereon by the built structures and byoverlying and adjacent soil masses; and determining attainment of aidminimum compaction value required by constantly monitoring levelvariations of the soil surface and/or of the built structure overlyingsaid injection zone to detect a moment when the built structure and/orthe soil surface, overlying said injection zone, begins to raise, whichis the moment when the soil lying below and around said injection zonewithstands and rejects upwardly the dynamic and static weight exertedthereon by said built structures and overlying and adjacent soil masses.21. The method of claim 20, wherein the built structures include any of:buildings, roadway slabs, airport runaways, and equipment supportingslabs.
 22. A method for increasing the bearing capacity of foundationsoils for built structures comprising: establishing appropriatetreatment levels located at different depths in a foundation soilrequiring bearing capacity increasing, said foundation soil being atleast that part of soil having to withstand dynamic and static weightsexerted by a built structure and by overlying and adjacent soil masses;providing a plurality of hole spaced from each other deep in thefoundation soil so as to reach said treatment levels; providing anexpandable substance with very fast expansion time and with a potentialincrease in volume of the expanded substance being at least five timesthe volume of the substance before expansion; injecting into the soil,through said holes said substance which expands as a consequence of achemical reaction; producing compaction of the soil contiguous to eachsubstance injection zone by way of the expansion of said sub injectedinto the foundation soil; and estimating the bearing capacity achievedin the foundation soil treated with expanding substance injections byconstantly monitoring the level of the soil surface and/or builtstructure overlying the in injection zone to detect a moment when thebuilt structure and/or the soil surface, overlying zone, begins to raisewhich is the moment when the compaction of the soil due to the substanceexpansion has reached levels generally higher a required minimum valueat which the soil lying below and around said injection zone withstandsand rejects dynamic and static weights exerted thereon by said builtstructures and by overlying and adjacent soil masses.
 23. A method forincreasing the bearing capacity of foundation soils for built structurescomprising: establishing appropriate eat levels located at differentdepths in a foundation soil requiring bearing capacity increasing, saidfoundation soil being at least that part of soil withstanding dynamicand tic weights exerted by a built structure and by overlying andadjacent soil masses; providing a plurality of ho spaced from each otherdeep in the foundation soil so as to reach said treatment levels;providing an expandable balance with very fast expansion time and with apotential increase in volume of the expanded substance being at leastfive times the volume of the substance before expansion; injecting intothe soil, through said holes, a quantity of said substance which expandsas a consequence of a chemical reaction; producing compaction of soilcontiguous to the substance injection zone by way of the expansion ofsaid quantity of substance injected into the foundation soil until thesoil compaction reached levels which are generally higher than a minimumcompaction value requiring to provide a bearing capacity of thefoundation soil suitable to withstand any dynamic and static weightexerted thereon by the built structures and by overlying and adjacentseen soil masses; and detecting reaching of said urn compaction valuerequired by constantly monitoring level variations of the soil surfaceand/or of kite built structure overlying said injection zone to detect amoment when the built structure and/or the soil surface, overlying saidinjection zone, begins to raise, which is the moment when the soil lyingbelow and around said injection withstands and rejects upwardly thedynamic and static weight exerted thereon by said built structures andoverlying and adjacent soil masses; and carrying out said expendablesubstance injection at said treatment levels at least until said minimumcompaction value detected through said monitoring is reached.